THE ORAL CAVITY. 



251 



tentacular cells. The cavities are often 10 ft in depth, and are 

 filled with a fluid apparently in communication with the fluid of 

 the depression into which the circumvallate papillae are sunk. The 

 processes of the neuro-epithelial cells project into the cavity from 

 its floor and lateral walls, but do not extend as far as the taste- 

 pore. 



The circumvallate papillae are differentiated from the adjacent 

 surface of the tongue by the development of a solid encircling 

 epithelial ridge. Nu- 

 merous taste-buds ap- 

 pear on the surface 

 quite early in the his- 

 tory of the embryo. 

 These, however, dis- 

 appear completely 

 when the permanent 

 taste - buds develop 

 from the basal cells 

 of the epithelial ridge. 

 Similar phenomena 

 occur in the fungiform 

 papillae (Hermann, 



Tegmental 



cell. 



_ Neuro-epithe- 

 lial cell. 



Sustentacular 

 cell. 



Terminal 

 branches of 

 nerves. 



Fig. 195. Schematic representation of a taste-goblet 

 (partly after Hermann, 88). 



The neural epith- 

 elia of the taste-gob- 

 lets were formerly re- 

 garded as directly 

 connected with the 



nerve-fibers by means of long processes, but the latest researches 

 have shown that dendrites of sensory neurones (sensory nerves) 

 enter the taste-buds and end free in telodendria. The latter sur- 

 round the neuro-epithelial and, to some extent, the sustentacular 

 cells, their relations depending upon contact. 



The Lymph-follicles of the Tongue (Folliculi linguales) 

 and the Tonsils. At the root of the tongue, and especially at its 

 sides, are numerous elevations due to the increased quantity of 

 lymphoid tissue found in the mucosa of these regions, the lingual 

 tonsils, or lingual follicles. In the center of each follicle is a cavity 

 communicating with the exterior and caused by an invagination of 

 the epithelium. The lymphoid tissue contains a number of more or 

 less distinctly defined lymph-nodules, some even showing germ 

 centers (vid. p. 197). The whole structure is surrounded by a 

 connective-tissue capsule. The epithelial walls of the follicular 

 cavities often show extensive degenerative changes, which are 

 accompanied by increased migration of leucocytes into the oral 

 cavity. These leucocytes change (according to Stohr, 84) into the 

 so-called mucous or salivary corpuscles of the saliva. 



Pharyngeal Tonsil. The pharyngeal tonsils may be regarded 



